chore: port PRs pointed at v0.1.x to master

tracing-subscriber/src/fmt/fmt_subscriber.rs

@@ -68,6 +68,7 @@ pub struct Subscriber<C, N = format::DefaultFields, E = format::Format, W = fn()
     fmt_event: E,
     fmt_span: format::FmtSpanConfig,
     is_ansi: bool,
+    log_internal_errors: bool,
     _inner: PhantomData<fn(C)>,
 }
 
@@ -117,6 +118,37 @@ where
             fmt_span: self.fmt_span,
             make_writer: self.make_writer,
             is_ansi: self.is_ansi,
+            log_internal_errors: self.log_internal_errors,
+            _inner: self._inner,
+        }
+    }
+
+    /// Updates the event formatter by applying a function to the existing event formatter.
+    ///
+    /// This sets the event formatter that the subscriber being built will use to record fields.
+    ///
+    /// # Examples
+    ///
+    /// Updating an event formatter:
+    ///
+    /// ```rust
+    /// let subscriber = tracing_subscriber::fmt::subscriber()
+    ///     .map_event_format(|e| e.compact());
+    /// # // this is necessary for type inference.
+    /// # use tracing_subscriber::Subscribe as _;
+    /// # let _ = subscriber.with_collector(tracing_subscriber::registry::Registry::default());
+    /// ```
+    pub fn map_event_format<E2>(self, f: impl FnOnce(E) -> E2) -> Subscriber<C, N, E2, W>
+    where
+        E2: FormatEvent<C, N> + 'static,
+    {
+        Subscriber {
+            fmt_fields: self.fmt_fields,
+            fmt_event: f(self.fmt_event),
+            fmt_span: self.fmt_span,
+            make_writer: self.make_writer,
+            is_ansi: self.is_ansi,
+            log_internal_errors: self.log_internal_errors,
             _inner: self._inner,
         }
     }
@@ -152,6 +184,7 @@ impl<C, N, E, W> Subscriber<C, N, E, W> {
             fmt_event: self.fmt_event,
             fmt_span: self.fmt_span,
             is_ansi: self.is_ansi,
+            log_internal_errors: self.log_internal_errors,
             make_writer,
             _inner: self._inner,
         }
@@ -235,6 +268,7 @@ impl<C, N, E, W> Subscriber<C, N, E, W> {
             fmt_event: self.fmt_event,
             fmt_span: self.fmt_span,
             is_ansi: self.is_ansi,
+            log_internal_errors: self.log_internal_errors,
             make_writer: TestWriter::default(),
             _inner: self._inner,
         }
@@ -249,6 +283,58 @@ impl<C, N, E, W> Subscriber<C, N, E, W> {
             ..self
         }
     }
+
+    /// Sets whether to write errors from [`FormatEvent`] to the writer.
+    /// Defaults to true.
+    ///
+    /// By default, `fmt::Subscriber` will write any `FormatEvent`-internal errors to
+    /// the writer. These errors are unlikely and will only occur if there is a
+    /// bug in the `FormatEvent` implementation or its dependencies.
+    ///
+    /// If writing to the writer fails, the error message is printed to stderr
+    /// as a fallback.
+    ///
+    /// [`FormatEvent`]: crate::fmt::FormatEvent
+    pub fn log_internal_errors(self, log_internal_errors: bool) -> Self {
+        Self {
+            log_internal_errors,
+            ..self
+        }
+    }
+
+    /// Updates the [`MakeWriter`] by applying a function to the existing [`MakeWriter`].
+    ///
+    /// This sets the [`MakeWriter`] that the subscriber being built will use to write events.
+    ///
+    /// # Examples
+    ///
+    /// Redirect output to stderr if level is <= WARN:
+    ///
+    /// ```rust
+    /// use tracing::Level;
+    /// use tracing_subscriber::fmt::{self, writer::MakeWriterExt};
+    ///
+    /// let stderr = std::io::stderr.with_max_level(Level::WARN);
+    /// let subscriber = fmt::subscriber()
+    ///     .map_writer(move |w| stderr.or_else(w));
+    /// # // this is necessary for type inference.
+    /// # use tracing_subscriber::Subscribe as _;
+    /// # let _ = subscriber.with_collector(tracing_subscriber::registry::Registry::default());
+    /// ```
+    pub fn map_writer<W2>(self, f: impl FnOnce(W) -> W2) -> Subscriber<C, N, E, W2>
+    where
+        W2: for<'writer> MakeWriter<'writer> + 'static,
+    {
+        Subscriber {
+            fmt_fields: self.fmt_fields,
+            fmt_event: self.fmt_event,
+            fmt_span: self.fmt_span,
+            is_ansi: self.is_ansi,
+            log_internal_errors: self.log_internal_errors,
+            make_writer: f(self.make_writer),
+            _inner: self._inner,
+        }
+    }
 }
 
 impl<C, N, L, T, W> Subscriber<C, N, format::Format<L, T>, W>
@@ -276,6 +362,7 @@ where
             fmt_span: self.fmt_span,
             make_writer: self.make_writer,
             is_ansi: self.is_ansi,
+            log_internal_errors: self.log_internal_errors,
             _inner: self._inner,
         }
     }
@@ -288,6 +375,7 @@ where
             fmt_span: self.fmt_span.without_time(),
             make_writer: self.make_writer,
             is_ansi: self.is_ansi,
+            log_internal_errors: self.log_internal_errors,
             _inner: self._inner,
         }
     }
@@ -419,6 +507,7 @@ where
             fmt_span: self.fmt_span,
             make_writer: self.make_writer,
             is_ansi: self.is_ansi,
+            log_internal_errors: self.log_internal_errors,
             _inner: self._inner,
         }
     }
@@ -433,6 +522,7 @@ where
             fmt_span: self.fmt_span,
             make_writer: self.make_writer,
             is_ansi: self.is_ansi,
+            log_internal_errors: self.log_internal_errors,
             _inner: self._inner,
         }
     }
@@ -462,6 +552,7 @@ where
             make_writer: self.make_writer,
             // always disable ANSI escapes in JSON mode!
             is_ansi: false,
+            log_internal_errors: self.log_internal_errors,
             _inner: self._inner,
         }
     }
@@ -528,6 +619,38 @@ impl<C, N, E, W> Subscriber<C, N, E, W> {
             fmt_span: self.fmt_span,
             make_writer: self.make_writer,
             is_ansi: self.is_ansi,
+            log_internal_errors: self.log_internal_errors,
+            _inner: self._inner,
+        }
+    }
+
+    /// Updates the field formatter by applying a function to the existing field formatter.
+    ///
+    /// This sets the field formatter that the subscriber being built will use to record fields.
+    ///
+    /// # Examples
+    ///
+    /// Updating a field formatter:
+    ///
+    /// ```rust
+    /// use tracing_subscriber::field::MakeExt;
+    /// let subscriber = tracing_subscriber::fmt::subscriber()
+    ///     .map_fmt_fields(|f| f.debug_alt());
+    /// # // this is necessary for type inference.
+    /// # use tracing_subscriber::Subscribe as _;
+    /// # let _ = subscriber.with_collector(tracing_subscriber::registry::Registry::default());
+    /// ```
+    pub fn map_fmt_fields<N2>(self, f: impl FnOnce(N) -> N2) -> Subscriber<C, N2, E, W>
+    where
+        N2: for<'writer> FormatFields<'writer> + 'static,
+    {
+        Subscriber {
+            fmt_event: self.fmt_event,
+            fmt_fields: f(self.fmt_fields),
+            fmt_span: self.fmt_span,
+            make_writer: self.make_writer,
+            is_ansi: self.is_ansi,
+            log_internal_errors: self.log_internal_errors,
             _inner: self._inner,
         }
     }
@@ -541,6 +664,7 @@ impl<C> Default for Subscriber<C> {
             fmt_span: format::FmtSpanConfig::default(),
             make_writer: io::stdout,
             is_ansi: cfg!(feature = "ansi"),
+            log_internal_errors: false,
             _inner: PhantomData,
         }
     }
@@ -660,6 +784,11 @@ where
             {
                 fields.was_ansi = self.is_ansi;
                 extensions.insert(fields);
+            } else {
+                eprintln!(
+                    "[tracing-subscriber] Unable to format the following event, ignoring: {:?}",
+                    attrs
+                );
             }
         }
 
@@ -806,7 +935,20 @@ where
                 .is_ok()
             {
                 let mut writer = self.make_writer.make_writer_for(event.metadata());
-                let _ = io::Write::write_all(&mut writer, buf.as_bytes());
+                let res = io::Write::write_all(&mut writer, buf.as_bytes());
+                if self.log_internal_errors {
+                    if let Err(e) = res {
+                        eprintln!("[tracing-subscriber] Unable to write an event to the Writer for this Subscriber! Error: {}\n", e);
+                    }
+                }
+            } else if self.log_internal_errors {
+                let err_msg = format!("Unable to format the following event. Name: {}; Fields: {:?}\n",
+                    event.metadata().name(), event.fields());
+                let mut writer = self.make_writer.make_writer_for(event.metadata());
+                let res = io::Write::write_all(&mut writer, err_msg.as_bytes());
+                if let Err(e) = res {
+                    eprintln!("[tracing-subscriber] Unable to write an \"event formatting error\" to the Writer for this Subscriber! Error: {}\n", e);
+                }
             }
 
             buf.clear();
@@ -1105,6 +1247,69 @@ mod test {
         re.replace_all(s.as_str(), "timing").to_string()
     }
 
+    #[test]
+    fn format_error_print_to_stderr() {
+        struct AlwaysError;
+
+        impl std::fmt::Debug for AlwaysError {
+            fn fmt(&self, _f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+                Err(std::fmt::Error)
+            }
+        }
+
+        let make_writer = MockMakeWriter::default();
+        let subscriber = crate::fmt::Collector::builder()
+            .with_writer(make_writer.clone())
+            .with_level(false)
+            .with_ansi(false)
+            .with_timer(MockTime)
+            .finish();
+
+        with_default(subscriber, || {
+            tracing::info!(?AlwaysError);
+        });
+        let actual = sanitize_timings(make_writer.get_string());
+
+        // Only assert the start because the line number and callsite may change.
+        let expected = concat!(
+            "Unable to format the following event. Name: event ",
+            file!(),
+            ":"
+        );
+        assert!(
+            actual.as_str().starts_with(expected),
+            "\nactual = {}\nshould start with expected = {}\n",
+            actual,
+            expected
+        );
+    }
+
+    #[test]
+    fn format_error_ignore_if_log_internal_errors_is_false() {
+        struct AlwaysError;
+
+        impl std::fmt::Debug for AlwaysError {
+            fn fmt(&self, _f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+                Err(std::fmt::Error)
+            }
+        }
+
+        let make_writer = MockMakeWriter::default();
+        let subscriber = crate::fmt::Collector::builder()
+            .with_writer(make_writer.clone())
+            .with_level(false)
+            .with_ansi(false)
+            .with_timer(MockTime)
+            .log_internal_errors(false)
+            .finish();
+
+        with_default(subscriber, || {
+            tracing::info!(?AlwaysError);
+        });
+        let actual = sanitize_timings(make_writer.get_string());
+        assert_eq!("", actual.as_str());
+    }
+
     #[test]
     fn synthesize_span_none() {
         let make_writer = MockMakeWriter::default();